Explicação do forense sobre o modo Lab do preto e branco…

Forensic Photoshop Tutorial – Sharpening in LAB mode

I’ve received a few e-mails from folks asking for a demonstration on sharpening in LAB mode. With this technique, we are going to be targeting just the Lightness Channel – affecting only the lightness values in the image.

In today’s image, detail is important. In a structural failure such as this, I want to highlight the sources of that failure. In this case, the bridge’s details, the torn and twisted metal, the bent rebar, and the broken concrete all have a part to play in the telling of this story. I also want to make sure that the items in the water receive attention.

Forensic Photoshop Tutorial - Sharpening in LAB mode

To begin, work the image as normal (focus correction, global light/colour, local light/colour) until you come to the Creative Sharpening stage. If you’ve performed the previous corrections in RGB, save the layered file before moving into LAB mode (Image>Mode>Lab Color). If you moved to LAB mode before making the initial corrections, continue on.

I mentioned earlier that we will be working with the lightness values only. Here’s how it works:

  1. Press Ctrll+Alt+1 to select only the lightness values.
  2. Invert the selection – Shift+Ctrl+I.
  3. Click Ctrl+H to hide the selection.
  4. With the Channels Palette open, select the Lightness Chanel.

Forensic Photoshop Tutorial - Sharpening in LAB mode

Selecting the Unsharp Mask filter (Filter>Sharpen>Unsharp Mask) brings up this dialog. For today’s image, I’ve used Amount=150, Radius=3, and Threshold=2. You can toggle the Preview button on/off to preview the results.

Forensic Photoshop Tutorial - Sharpening in LAB mode

When you’ve finished applying the filter, click Ctrl+D to deselect the lightness values (remember, you hid them earlier). Continue on with the workflow (saving as necessary).

When you are finished, you’ll see that the difference can be quite dramatic.

Forensic Photoshop Tutorial - Sharpening in LAB mode

Try this one for yourself. You’ll be glad you’ve added LAB sharpening to your tool box.

Fonte: photoshopsupport

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